1991 chevy blazer 4.3 problems that come and go.

[t160hq]

Ok here's the low down. Jumped into my trusty Blazer this morning to go to work. Started just fine as it has for the last 9 years. Started down the road then the trouble started. It was missing. sputtering, backfiring through the tunnel port so bad in fact that it blew the cover off the air cleaner.

Got on the highway and managed to get it up to 60 but every time you punched it same symptoms. Damn near died when you feed it the gas.

Well decided to run it back home and take the other car. Bewteen stalls and getting it started again i finally managed to get it back. About 10 miles.

Got home tonight. Got out the engine cleaner and the pressure washer to clean up the engine. I just hate to work on a dirty engine. Cleaned her all up. Started it up to take it for a spin to dry off the engine. Ran great. No problems.

Any ideas? I was all geared up with no bolts to turn. I just don't know where to go from here.

t160hq

[Chief]

A few things come to mind....
1) Mass airflow sensor
2) EGR valve sticking
3) Pickup coil in distributor
4) Ignition module in distributor

You said "tunnel port", but I don't know if you have the Vortec induction system or the throttle body FI. The throttle bodies can get carboned up and make it run rough as hell....but normally, it doesn't come and go....it just comes and stays.

An ECM scan with a GOOD scanner should pinpoint it...it will save you LOTS of diagnostic time, believe me. Did it set a code? (turn on service engine soon light?)
I have seen these 4.3 Blazers run fine until they warm up...any of the above four problems can be brought on by heat....makes 'em even more difficult to do a shadetree diagnosis. As you said, after it cooled down, the problem disappeared.

[mdeven]

See if you can borrow a real time scan tool such as Snap-On makes.... Drive it for a while with it hooked up.... They are capable of making a "movie" of sorts....
Chief is correct, that engine (unless modified) has TBI....
My first guess would be the EGR valve....
Mark

[lefty]

Ok here's the low down. Jumped into my trusty Blazer

FWIW, when my 93 4.3L EGR valve failed, it did not do any of the things you described.

How long since the the last tuneup and fuel filter?

:cool:

[t160hq]

Yes it is throttle body FI. I should be more exact.

Last tune up was six months ago. Changed the fuel filter at the same time. New plugs. Old wires and distributor cap. About 50,000 miles on those.

I'll give the EGR valve a shot. Thanks.

If it makes a difference the engine has 270,000 miles on it. No major repairs. Just the minor stuff fuel pump (about two years ago) Water pump, alternator that sort of thing.

Did check the compression last night. All the cylinders were within 15% of each other.

I do get a bit of smoke at start up. But it's been doing that for the last 4 years.

No check engine light when acting up. No codes stored.

What about a flaky O2 sensor? It's the orginal that came with the car. I would think I would get a stored code if that was acting up?
t160hq

[4x4]

If I was you I would go to an auto store and buy a code reader ..
It is just a little box that plugs in under the dash and will tell you if you have problems .. Not all problems but most ... On your vehicle you will see a port just above where you right knee is and it will plug in there ...
Check this link below , they all look the same and the price may vary ...
I always use it before I go for my polution test ...

http://www.iequus.com/partinfo.asp?PartNumber=3123

[HotRodTodd]

My friend Jim just brought his 92 safari van to my shop last week with the same symptoms. He's a pretty good mechanic and had changed about everything you can think of that would give those symptons. I checked it out with the laptop and no codes stored. Drove it let it idle, drove it again, still no codes. On his 4.3 there is no port to hookup a fuel pressure guage to the throtle body so i rigged up a hose and guage to the return line to see what was going on. Well the fuel pressure regulator is built into the tbi and that was the cause of the problem. It was bleeding off the fuel pressure prematurely causing it to lean itself out. Took the regulator apart, cleaned the tbi real good, replaced the guts of the regulator and no more problems. You may have the same problems, just something you might want to look at also. Good Luck.

[t160hq]

Thanks HotRodTodd. Sounds like a very good first step. At least it won't involve a lot of expensive parts that may not fix it.

Already have a code reader 4x4. One of those plug in jobs with the blinking light. That's how I found out no codes were stored. I also have all the GM manuals for this beast. Got everything I need for the job just with a intermitten like this I did not know where to start looking.

I was checking to see if someone like HotRodTodd had run into this sort of thing before and he did!

t160hq



t160hq

[4x4]

OK , this happened to me once , I had dirt in the fuel tank but didn't know it .. So I would drive so far and the thing would start to run shity and then die .. Let er sit for a bit and now it runs again , go a little farther and it dies .. The screen on the fuel pickup in the tank was picking up all the dirt , when the motor was shut off the suction stopped and the dirt sank to the bottom again , start it back up and it would go through the whole process ..
Electric fuel pumps just die there is no running crappy with them , they either work or they don't ...

[mili]

1,Put a plastic bag in the fuel tank. When the pump sucks it in the engine dies.
2,Engine stalls, the vacuum is gone and the bag settles to the botom.
3, Goto 1

mili

[t160hq]

It is the same symptoms as when the first fuel pump went out. Except the backfire through the TBI. That didn't happen the first time the fuel pump went out.

That pump was replaced two years ago. Is it common for replacement pumps to fail that quickly? The first one lasted 7 years.

Any way of testing it off the car?

t160hq

[t160hq]

Or on the car for that matter. Hook some kind of pressure guage up and monitor it while in operation.

t160hq

[lefty]

Put a plastic bag in the fuel tank.

I've fished some strange items out of diesel fuel tanks:

sponge
plastic cups
red rags
strings
plastic bags
sawdust
rust
water
piss (yech!)
candy wrappers
rubber balls

All caused our customers to cuss us.
All were caused by customers employees.

:snipersmi

:cool:

[HotRodTodd]

I have had this same problem and I change everything to find out that I had a burnt valve. It ran fine some days and others like chit. Some days I put it in gear and it die. I worked on it for 2 weeks.

He did a compression test first which eliminates that as being the problem.

[t160hq]

Update. Since I had the time and it needed a few other maintence items done decided to tear a few things down and check them out.

Pulled the gas tank and checked inside. No cantaminents of any type. Clean as a whistle.
Changed the fuel pump. Not sure it was actually bad just the most likely suspect. Changed the fuel filter.

Checked the timing chain and gears. Looked good no damage at all. Very little wear. I was actually stunned after that many miles that they looked that good.

Did not take out the cam and get out the micrometer and check it out. The chain and gears looked so good dismissed it as a possiablity.

Took off the TBI unit and cleaned it to within a inch of its life and replaced everything replacable. reasembled and reinstalled.

Cleaned and painted the air cleaner housing. Really don't think this will make a difference but it was starting to look like crap. *grin*

Checked the fuel pump relay. Yea I didn't know it even had one till i looked in the manual. Looks fine no burnt contacts and good voltage to it.

Been running for three days no problem. Not sure what cured it but if it runs ok for another week I'm gonna declare it fixed.

Thanks guys!

t160hq

[mdeven]

My money's on the new paint....
Mark

[jrsgta]

thats why mr. goodwrench had over 100,000,000 in training last year....thats wat the guy on tv said

[HotRodTodd]

My money's on the new paint....
Mark

LOL, yeah the paint is my bet too! Should be good for at least another 30hp increase also ;)

[mdeven]

LOL, yeah the paint is my bet too! Should be good for at least another 30hp increase also ;)
Maybe the fumes :D
Mark

[lefty]

Ya'll can josh all ya want, but I have it on good authority (truck drivers) that chrome makes a truck go faster, so maybe, just maybe that paint helped!

:) ;) :eek13:

[t160hq]

Sprang for the delco pump. Took a look at the replacement line pump but it looked kinda cheap and nasty. No checkers in our area so I may have overpaid a bit. But from past experience I've found OEM parts just hold up better.

t160hq

[mdeven]

Ya'll can josh all ya want, but I have it on good authority (truck drivers) that chrome makes a truck go faster, so maybe, just maybe that paint helped!

:) ;) :eek13:

Why does everybody blame stupid shit on us?
Mark